Reverse total shoulder arthroplasty component center of rotation affects muscle function

Area of Science:

• Orthopedic Surgery
• Biomechanical Engineering
• Musculoskeletal Modeling

Background:

• Glenosphere medialization impacts deltoid function and increases scapular notching risk.
• Understanding glenosphere positioning is crucial for optimizing shoulder arthroplasty outcomes.

Purpose of the Study:

• To evaluate the effect of glenosphere position on deltoid muscle efficiency.
• To assess the influence of glenosphere placement on glenohumeral adduction range.

Main Methods:

• Virtual implantation of total shoulder arthroplasty on 3D bone models.
• Simulation of varying glenosphere medialization and inferior placement.
• Musculoskeletal modeling to compute muscle and joint forces during abduction.

Main Results:

• Superior or lateral glenosphere placement elevated joint reaction forces.
• Deltoid muscle moment arm was greatest at the baseline surgical position.
• Glenosphere medialization affected glenohumeral adduction, with superior placement causing significant deficits.

Conclusions:

• Optimal glenosphere placement requires balancing implant stress, impingement, and deltoid efficiency.
• Partial glenosphere medialization emerges as a viable strategy to enhance deltoid function and reduce notching.